High capacity lifting systems involve rigging that frequently employ lines that are either high strength steel or the modern synthetic high strength lines. The synthetic lines with high strength fibers have advanced beyond available and suitable high strength thimbles. The thimbles are required to protect the synthetic and wire rope ends, termed eyes, from being crushed when the rope is attached to shackles or other connectors. The thimble's primary purpose is to control the rope eye radius under high loads. The strengths of some synthetic ropes have reached the capacity of steel ropes with the advantage of low weight. An example is a 3 inch diameter synthetic rope rated at nearly 900 metric tons breaking strength. While these modern ropes offer significant advantages due to their lighter weight and freedom from corrosions, they must be protected from abrasion. It is also important that the configuration of the eye be maintained geometrically to retain peak strength levels.
Apart from these issues it is very important to allow eyes previously braded into the ropes to be inserted into a thimble without the costly exercise of reforming the eyes by braiding. It is also beneficial if the eye can be retained within the thimble boundary without requiring manual lashing. Manual lashing requires materials that can be easily tom away or cut when dragged over a shop floor or job site with debris. Losing the braiding around the eye can allow damage to the eye and failure of the lifting rope creating safety issues and potential damage to equipment.